This invention relates to chucks for machine tools designed either for high-speed operation or machining operations in which the chuck must sustain severe lateral forces due to the machining pressures exerted on the workpiece. In either case, it is essential that the workpiece be positively held and that the grip on the workpiece is capable of positively resisting any forces, such as centrifugal forces, which would tend to cause it to loosen its grip on the workpiece. This latter requirement has become much more urgent and meaningful as both the operating speed and the pressure exerted by the tools on the workpieces have been increased.
The problem has been to satisfy the need for better and more positive engagement with the workpiece without materially increasing the cost of the chuck, limiting its utility or complicating its set-up procedure.
Heretofore chucks designed for the service conditions to which this invention is designed to be applied have been limited to a very small jaw movement capability. As a result, the chucks are highly specialized and have limited use and are not adaptable &:o use with workpieces of any significant range of dimensional difference without a long and complicated rework adjustment of the chuck. Since such chuck adaptation work must be done by skilled personnel, the cost of adaptation of the chuck from one job to another has been prohibitive unless the length of the run on which the chuck is to be used is of sufficient size that the cost of adaptation can be absorbed.
This invention overcomes this difficulty by providing means different from those described and claimed in the application above identified by which such chucks can be quickly adapted to serve a much wider range of workpiece sizes with a minimum downtime requirement without the necessity for use of highly skilled labor to perform the changeover. Like the invention described in our co-pending application, the changeover can be accomplished so rapidly that there is no reason to attempt to use the machine on which the chuck has been mounted for any other purpose while the changeover is being made. Further, this permits the chuck to be used for a much wider range of work and thus for a much higher proportion of its availability. This materially expands the basis upon which the capital investment in the chuck can be amortized and also reduces the number of chucks which a machine shop has to keep in inventory in order to have a reasonable spectrum of capability. The invention also materially reduces the amount of machine tool downtime necessary for changeover from one machining job to another. For smaller machine shops, it significantly increases the scope and range of the jobs the machine shop can profitably perform with each of its chucks. Thus, the chuck's return on capital is materially increased and the requirements of storage space for idle chucks is significantly reduced.
Another aspect of this invention is its use with chucks having so-called soft jaws, that is, chucks having jaws of unhardened steel. These are desirable for many machining operations. This invention permits such jaws to have a much longer service life before major reconditioning since the wear on the jaws can be compensated simply by adjusting the outer jaws' position with respect to the inner jaw by means which are quick and simple to use.
A further aspect to this invention is that it provides a positive means of preventing the chuck changeover being considered complete without the outer jaw being positively locked to the inner jaw. Failure to lock the jaws together can result in serious injury to personnel and the equipment. This invention provides positive physical evidence that this step has not been completed. It prevents the tool used both to release and to secure the outer jaw from being removed from the chuck unless the outer jaw has been properly secured.